Radio broadcasting



Patented July 16, 1935 v UNITED STATES 'PAT ' RADIO BROADCASTING WilliamA Mueller, Hollywood, Calif., assignor to United Research Corporation,Long Island City, N. Y., a corporation of Delaware Application June19,1933, Serial No. 676,461

6 Claims.

The invention relates to broadcasting, wherein a radio wave is modulatedin accordance with the currents from a plurality of microphone circuits.

In broadcasting a football game, for example, use may be made of thefolowing microphone circuits; first, the announcers microphone which isusually installed in .a sound-proof booth, and which may be termed themain microphone, and 1 second, one or more auxiliary microphones such asa microphone for the cheering sections, a microphone to reproduce thecrowd noise, and a microphone with parabolic or other sound waveconcentrator which may be pointed toward the players to selectively pickup a desired portion of the play.

Heretofore in using main and auxiliary microphones as pointed out above,it has been customary for the monitor to manually regulate the vol umeof the currents in the different microphone circuits. This method ofcontrol results in broad- -casting an irregular volume of audio currentbecause it is impossible to manually regulate all of the microphonecircuits in such a way that the total volume of the current thereinshall at all times be constant, and what is more important, theannouncer cannot always be understood at the receiving station for thereason that it is not possiblefor the monitor to instantly suppress the30 current in the auxiliary circuits when the announcer speaks.

These defects are overcome according to the present invention byproviding method and means for automatically and instantaneouslyregulating the current in the auxiliary microphone circuits inaccordance with the current in the announcer microphone circuit, wherebythe announcer microphone circuit, when audio currents are presenttherein, serves to instantly reduce to a desired level the volume of theaudio currents in the auxiliary microphone circuits, the currents in theauxiliary microphone circuits instantly being restoredto normal upon thecessation of audio currents in the announcer microphone circuit. Whilesatisfactory results are obtained by controlling the main microphoneinstantly by the auxiliarymicrophones, or vice versa, that is withoutany appreciable delay, it has been found that improved results areobtained by delaying the effectiveness of the controlling arrangementfor a very brief interval of time, such as a fraction of a second.Experience has shown that if the volume or level of the current 1 in theauxi1iarymicrophone circuits is varied too rapidly by the ,current inthe main microphone circuit, the change would be noticeable at thebroadcast receiving station. Also, if the level is changed too s1owly,this would be noticeable. Accordingly, the speed of operation is delayeda selected amount, i.-e'. for a fraction of a second, whereby thevariation in the level'of the auxiliary microphone current is notnoticeable at the receiving station.

A further object of the invention is 'to' prevent the amplifier in theauxiliary microphone circuit from giving rise to noise currents attimeswhen the auxiliary microphone currents are suppressed by theannouncer microphone control. Thisjis accomplished by employing asuppressor grid type tube in the amplifier for the auxiliary microphone. Also, in case the announcers microphone or other pickup device isnot enclosed in a soundproof booth but is employed ina location wherethere may be extraneous low frequencysounds,

such as door slams or heavy footsteps, such ex traneous sounds areprevented from exertingany control on the auxiliary microphone circuitby employing in the control circuit an amplifier which is relativelyinsensitive to such low fre quency sounds, whereby the whole controllingeffect is due to the audio currents corresponding to the announcersvoice or the like. f

For further details of the invention reference may be made to thedrawing, wherein:

Fig. 1 is a diagrammatic view of a preferred circuit arrangement. i

Fig. 2 is a schematic view of a radio broadcasting circuit embodying thecircuit of Fig.1. Referring to Fig. 2, there is provided a. mainmicrophone I for the use of the announcer. This microphone may or maynot be housed in a sound proof booth as pointed out above. There arealso provided one or more auxiliary microphones, such as 2 which may beused for the cheering section,

3 for the crowd noise, and 4 a concentrator microphone which can bepointed to pick up sound waves from a desired source, such as theplayers.

Current from the microphone I and from one or more of theauxiliarymicrophones'2,'3, and 4, after being amplified by the amplifier 5 issent over the transmission line 6 to the radio. broadcasting stationwhereis located the high frequency generator! and a modulator 8 for modulating the radio waves from generator I in accordance with the audiofrequency currents derived from or furnished by the microphones I, 2, 3and. 4. The radio wave thus modulated is radiated by antenna 9. a

" The volume of current fromthe microphones .I to 4' inclusive may bemanually regulated'by rectified is supplied to, the amplifier I4 inorder to lating amplifier because it is uni-directional in preventingcurrent from amplifier I4 from being fed into the amplifier I and therectifier II. The input of amplifier I6. includes. a transformer I8, theinput coil II! of which is split and connected through a m. f. condenser23 in. order to provide reduced transmission below a frequency of 250cycles and normal transmission 'of the audio frequency current frommicrophone I is amplified by amplifier I5 and supplied throughamplifier'i. to modulator 8, while another portion of the audiofrequency current from microphone I is amplified by. amplifier I6 and"supplied to the rectifier II. The current thus suppress the presence oramplification of current from the microphones 2, 3 and 4. when theannouncer is speaking in the microphone I, and to restore theamplification of audio current from themicrophones 2, 3 and 4 to normalwhen the announcer ceases to. speak in the microphone I, as pointed outabove.

Details of the arrangement for controlling the amplifier I4 inaccordance with the audio frequencycurrent. rectified by rectifier IIare illustratedin Fig. 1, wherein the auxiliary microphonesf2,,3 and 4are also: illustrated .as being connected in parallelto the input ofamplifier I4, theoutput of which leads to the antenna 9. In

' Fig. 1 it will be understood that the amplifier 5,

transmission line 6, generator I,.modulator Band isolating amplifier I5have been omitted as. the details of construction thereof are wellunderstood in the art and form no. part per se of the present invention.r.

In'Fig. 1. the microphones 2, 3, and 4-a1'econ- Y nected in parallel tothe primary coil of transformer 2|, the secondary coil of which isconnectedtothe grid 22 and the heater type cathode 23. In shunt to thissecondary coil is-a high resistance 24 which may be of about200,000ohms. The. grid 22 is biased negatively by the battery 25 andalso by: the potential across potentiometer ZE hichpotential resultsfrom rectified audio frequency current in the output circuit of" recti-V fier Hi The battery 25 and the potentiometer 26 are shunted bycondenser 21 of about 2 m. f.

The tube I4 is known as suppressor grid variable mu type tube 58 and hasthe advantage pointednout above that, when the biasing potential atpotentiometer 26 is high enough to reduce ,the amplification of thistube to "a negligible quantity, this tube remainssubstantiallynoiseless, and in fact it is noiseless also at normal values of gridbias. The suppressor grid 28 is connectedto the cathode lead 29.

Plate current is supplied to tube I4. over a cirthe variation in levelis not noticeable.

7 rent.

resistance 35 of about 10,000 ohms, the lead 36 I being tapped ofi fromresistance 35 so as to supply a positive potential of about 22 volts tothe shield grid 31. Between shield grid 31 and cathode lead 29 isshunted a condenser 38 of about 1 m. f. The output transformer 39 isconnected to the cathode lead 29 and'to theanode 30 through a stoppingcondenser 48. Theoutput transformer 39 is connected as illustrated inFig. 2 which generally represents between the lines 31:1: and yy theapparatus omitted between these lines in Fig. l.

Q'Ihe amplifier I6 is suitably coupled, for example through transformerM to the rectifier II, which comprises grid 42, cathode 43 and plate 44.The secondary coil of transformer 4| is connected 'to the grid 42 and toa suitable point in the re tifier II, meter 49 at the mixers position, Bbattery 50, resistance 5|, potentiometer 26 and cathode 43. In shuntbetween the'anode 44 .and cathode 43 at opposite sides of choke coil, 41are the condensers 52 and 53; As pointed outabove, the choke coil 41 andthe condensers 52 and 53 constitute a delay circuit for delaying thecontrol of amplifier I4 by rectifier [1, whereby, for normal amounts ofreduction of current in amplifier" l4,

been found that a suitable, delay is obtaincdby using the followingvalues; coil 4I-'-232 h; condenser 52 -2 m. f.; condenser 53 2 m. f. l

The purpose of resistor 5 I, which is in the plate circuit of rectifierI I, is to flatten out the rectifier characteristic whereby therectified current output will be proportional to the inputvoltage to therectifier only up to some value,'such 252 volts, and thereafter afurther increase in the voltage on the rectifier will notresult in, anysubstantial increase in the rectified output cut- Consequently, asoftspoken voice at the microphone 1 corresponding to low input depressesthe amplified current from microphones 2, 3 and 4 a desired amount, anda louder sound at the microphone I does not needlessly depress thecurrents from microphones 2, 3 and 4 further.

In this operation, therefore, there is heard at the phone I and itfollows therefore that the mam,

wave from generator I is modulated simultaneously with currents from themain and auxiliary microphones in balanced relation. It. willibeunderstoodthat the depressing effect on amplifier I4 by rectifiedcurrents from rectifier I'I ceases when microphone I is not inoperation,

whereby the currents from microphones 2,, 3 and 4 are transmitted atnormallev'el.

Asthe amplifier I4 overloads. at a compare tively low level, in order toprevent harmonic distortion, this amplifier I4 is installed in the circuit at the point of lowest amplification. In other words, asillustrated this amplifier, I4 isithe first amplifier in theseriesbetween the microw phones 2, 3'and 4 and the modulator 8.

The amount that the variable gain amplifier reducesthelevel 'of thecurrents from micro;-

phones 2', 3 and 4 is controlled bythe settingof the potentiometer 26which may be, calibrated at 2 db. steps. The current through amplifier Mcan be reduced by the rectified current as much as 20 (12)., although 8or 10 db. is all that has been found necessary.

The potentiometer 54 in Fig. 2 is placed at the mixers position so thatthe mixer can use as much or as little automatic regulation as desired,or cut it out entirely.

Certain of the features disclosed herein, such as the arrangement fordelaying the control of the amplifier by rectified current, and the useof an amplifier having a lower gain at low frequencies than at otherfrequencies, as well as the use of a suppressor grid type amplifier, areuseful in sound recording circuits wherein the microphones are replacedby pickup devices for translating sound records into electric currentsand wherein the common output from the pickup circuits is led to arecorder. Claims generic to such features, also claims to such featuresspecifically applying to sound recording circuits are presented inapplicants co-pending application S. N. 684,669 filed August 11, 1933for Method and means for regulating balance between currents inassociated circuits.

Having thus described the invention, what is claimed as new and desiredto secure by Letters Patent is:

I claim:

1. The method of broadcasting wherein a radio wave is modulated bycurrent from an announcer microphone circuit and from an auxiliarymicrophone circuit, which comprises controlling the volume of thecurrent in said auxiliary microphone circuit in accordance with and inresponse to the volume of the current in said announcer microphonecircuit, delaying said controlling for a short interval of time, andtransmitting over a common carrier wave the modulating impulses fromsaid microphone circuits.

2. The method of broadcasting wherein a plurality of audio frequencycircuits are connected to a common modulator, which comprises modulatinga high frequency wave in accordance with the current in said pluralityof circuits, controlling the volume of the current in one of saidcircuits in accordance with and in response to the volume of the currentin another of said circuits and in delaying the effectiveness of saidcontrolling. V

3. Radio broadcasting circuit comprising the combination of a pluralityof audio frequency circuits, a common radio output circuit therefor fortransmitting a radio wave in accordance with current in said pluralityof audio frequency circuits, a rectifier, circuit connections wherebysaid rectifier is responsive to the current in one of said circuits forcontrolling the volume of the current in another of said circuits, and adelaying device in circuit with said rectifier for delaying saidcontrolling.

4. Radio broadcasting circuit comprising the combination of a pluralityof audio frequency circuits, a common radio output circuit therefor, anamplifier in one of said audio frequency circuits, said amplifier havinga lower gain at low frequencies than at other frequencies, a rectifierconnected to said amplifier and also connected to supply rectifiedcurrent to another of said audio frequency circuits for controlling thevolume of audio frequency currents in said other circuit.

5. A radio broadcasting circuit comprising an announcer microphonecircuit, an auxiliary microphone circuit, a modulator connected to saidcircuits, a high frequency generator connected to said modulator wherebysaid high frequency currents are modulated in accordance with audiofrequency currents from both of said microphone circuits, meansresponsive to the audio frequency currents in said announcer microphonecircuit for automatically maintaining a balanced relation between theannouncer microphone current and the current in said auxiliarymicrophone circuit, and means for delaying the establishment of saidbalanced relation.

6. Radio broadcasting circuit comprising the combination of a pluralityof audio frequency circuits, a modulator circuit in common thereto formodulating a high frequency wave in accordance with current from saidplurality of audio frequency circuits, an amplifier in one of said audiofrequency circuits, said amplifier having a lower gain at lowfrequencies than at other frequencies, and a rectifier connected to saidamplifier and also connected to supply rectified current to another ofsaid audio frequency circuits for controlling the volume of audiofrequency currents in said other circuit.

WILLIAM A. MUELLER.

